The manufacture of steel ingots through the use of cast iron molds is well known in the art. Referring first to FIG. 1, a typical prior art method and system for manufacturing steel ingots from molten steel will be generally described. A cast iron mold 1 of the desired size and shape is first supplied. The walls 2 and floor 3 of the cast iron mold 1 form a cavity 4 having an open top end for receiving molten steel, which can be poured into the cast iron mold 1 while at temperatures over 1,000 degrees Fahrenheit. Existing cast iron molds 1, and the corresponding ingot manufacturing methods, are specially designed to allow heat to dissipate from the molten steel evenly from all sides.
First, the molten steel is poured into the cavity 4 of the cast iron mold 1. As the poured steel cools within the cast iron mold 1, the steel goes from the molten state to a solid shape. Naturally, the steel contracts during the cooling process. Thus, in order to create a solid steel ingot of uniform shape and high integrity, manufacturers attempt to maintain a molten steel head which feeds the solidifying and shrinking ingot body so as to achieve an ingot that has a consistent/uniform shape with as few cracks and/or voids as possible.
In order to achieve a uniform thermal cooling of the molten steel, steel ingot manufacturers typically utilize an insulating material 5 to cover the top surface of the molten steel and the mold walls of the cast iron mold 1. The most common insulating material used in the industry to cover the mold walls is a rigid refractory hottop sideboard material, which is applied to the mold walls of the cast iron mold 1 as sideboards 7.
An insulating powder is typically applied to the top surface of the molten steel at the remaining interface between the air and the molten steel. The insulting powder is applied so as to form a layer having a uniform thickness across the top surface of the molten steel. The thickness of the insulating powder layer is dictated by the thermal conductivity properties of the cast iron mold 1 and other variables.
However, during the pouring process, molten steel can infiltrate through gaps and cracks between the rigid refractory hottop sideboard and the mold wall, and also through gaps and irregularities within the rigid refractory hottop sideboard.
As the molten steel cools (and naturally contracts) the material near the walls 2 of the cast iron mold 1 has a tendency to shrink away from the sides of the mold walls 2, thereby leaving behind a gap where steel and refractory defects and irregularities in the surface and shape of the steel ingot and may form exogenous and unwanted defects. These defect are commonly referred to in the art as “fins.”
These fins of steel create a defect in the ingot that either: (1) cause the entire ingot to be scrapped; or (2) require machining and/or grinding down of the ingot by hand to remove the fins from the ingot and correct the defect. This type of defect is believed to be the second largest cause of defects and loss of money in the manufacture of steel ingots in the melt shop at a steel mill. The cost to manufacture a steel ingot is approximately 50 cents per pound, and each steel ingot can cost $5,000.00. The excessive work to repair fin defects can cause the parts to be totally scrapped. In total this defect can cost a typical melt shop at a steel mill more than $1,000,000 per year.
In an attempt to remedy the “fin” problem, steel mills began to incorporate sideboards 7 into the cast iron mold 1. The sideboards 7 are typically connected to the sidewalls 2 of the cast iron mold 1 at or near the top of the cavity 4 that received the molten steel. Existing sideboards 7 are constructed of a rigid refractory material, such as ceramic fiber board. These sideboards are commonly referred to in the art as “hottops.”The exact height of the sideboard 7 is chosen so that when the molten steel is initially poured into the cast iron mold 4, the surface level of the molten steel bath is surrounded by the sideboard 7. Typically, the surface level of the molten steel bath is at about the midpoint of the height of the inner surface 8 of the sideboard 7. Therefore, as the molten steel contracts and moves down the inner surface 8 of the sideboard 7, it is intended that a clean transition at the edges of the cooled steel ingot be achieved, thereby eliminating and/or reducing the occurrence of fins.
Referring now to FIG. 2, a top view of a the prior art sideboard 7 connected to the sidewall 2 of the cast iron mold 1 is schematically illustrated. As can be seen, the inner surfaces 9 of the sidewalls 2 of the cast iron mold 1 are typically corrugated (i.e., have an undulating surface). The corrugated surface is utilized to in order to increase the surface area of the steel ingot to be formed, which in turn increases thermal cooling, thereby reducing manufacturing time. The outer surface 10 of the rigid sideboard 7 is formed to match the corrugation of the inner surface 9 of the sidewalls 2 of the cast iron mold 1. Nails 11 or other fasteners are typically used to hold the sideboard 7 in place.
However, with continued use, the contour of the inner surface 9 of the sidewalls 2 of the cast iron mold 1 (and/or the contour of the outer surface 10 of the sideboard 7) becomes irregular. If there is not a tight fit between the inner surface 9 of the sidewall 2 and the outer surface 10 of the sideboard 7, the molten steel may penetrate even the smallest gap between the two, thereby resulting in “fins” during the cooling process.
Thus, extensive efforts have been undertaken to try to ensure that the rigid sideboards 7 are perfectly fitted to the sidewalls 2 of the cast iron mold 1. This is generally achieved by requiring extremely tight tolerances for the size and shape of the outer surface 10 of the sideboard 7. The need for such tight tolerances exponentially increases the cost of manufacturing the sideboards 7. Nonetheless, even when the desired tolerances are achieved, “fins” continue to appear during the manufacturing process, especially over time and continued use the same cast iron mold.